Inconsistencies in scatterometer wind products based on ASCAT and OSCAT-2 collocations

Sea surface vector winds from multiple satellite scatterometers are especially useful for oceanic and atmospheric applications. On the one hand, the number of space-borne scatterometers is increasing in recent years. On the other hand, the homogenization of wind products from different scatterometers and producers remains a challenge, which potentially prevents the beneficial use of multiple scatterometers for numerical weather prediction, studying air-sea interactions or monitoring and forecasting the ocean. In this study, the inconsistencies in scatterometer wind products are analyzed and differences are attributed to the different aspects of scatterometer wind measurements and processing in order to guide further research towards consistent scatterometer wind products. More in particular, the collocated C-band MetOp/ASCAT and Ku-band SCATSAT-1/OSCAT-2 data allow a unique opportunity for close and abundant global collocations of different scatterometer wind products. The Ku-band wind data are independently produced by the Royal Netherlands Meteorological Institute (KNMI) and the Jet Propulsion Laboratory (JPL). The comparison shows that the KNMI OSCAT-2 wind product rejects more “poor” quality data than the JPL wind product, while both quality control (QC) schemes have merits
and may be combined in a future development. Furthermore, the JPL OSCAT-2 wind speeds differ generally more from the ASCAT winds than the KNMI OSCAT-2 winds, especially for wind speeds above 17 m/s. It is confirmed that the wind speed differences between C- and Ku-band scatterometers are mainly caused by the effect of Sea Surface Temperature (SST). While the wind direction characteristics of the OSCAT-2 wind products are closely related to the inversion algorithms used, the geophysical model function (GMF) used in the wind inversion is the dominant factor for the remarkable differences between OSCAT-2 wind speeds produced by
KNMI and JPL. The error characteristics and inconsistencies of ASCAT and OSCAT-2 wind products presented in this manuscript provide guidance for data users and will promote further improvements in the consistency of scatterometer wind products.